As an exhaust gas purification apparatus for an internal combustion engine, Japanese patent No. 2727906 discloses technique in which an exhaust passage of the internal combustion engine is bifurcated into two branch passages at its intermediate portion, and a NOx trap is arranged in each branch passage, so that the amounts or flow rates of exhaust gas flowing into these NOx traps can be alternately decreased to regenerate the NOx trapping abilities of the NOx traps.
In the specification of U.S. Pat. No. 5,956,949, there is disclosed a technique that includes two exhaust passages connected with the respective banks of cylinders of a V-type internal combustion engine, and a catalyst arranged in each of the exhaust passages, wherein one of the catalysts can be activated at an early time by increasing the amount of the exhaust gas flowing into the one catalyst at the startup of the internal combustion engine.
In Japanese patent application laid-open No. H8-121153, there has also been disclosed a technique that includes two exhaust passages connected with the respective banks of cylinders of a V-type internal combustion engine, and a catalyst arranged in one of the exhaust passages, wherein the catalysts can be activated in early time by making the exhaust gases discharged from both of the banks of cylinders flow into the catalysts at the startup of the internal combustion engine.
In Japanese patent application laid-open No. 2003-343244, there has further been disclosed a technique that includes two exhaust passages connected with the respective banks of cylinders of a V-type internal combustion engine, and a catalyst arranged in each of the exhaust passages, wherein the exhaust gases discharged from both of the banks of cylinders are caused to flow into the two catalysts in a serial manner at the startup of the internal combustion engine, whereby an upstream side one of the catalysts is activated at an early time.
In Japanese patent application laid-open No. H6-173666, there is disclosed a technique in which an exhaust passage of an internal combustion engine is bifurcated into two branch passages at its intermediate portion, and a catalyst is arranged in each branch passage, so that an exhaust gas is made to flow through the two catalysts in a serial manner or in a parallel manner.
In Japanese patent application laid-open No. 2002-129951, there is disclosed a construction that includes two exhaust passages connected with the respective banks of cylinders of a V-type internal combustion engine with a three-way catalyst and an NOx storage and reduction type storage reduction catalyst being arranged in each exhaust passage.
In Japanese utility model laid-open No. S63-78118, there is also disclosed a construction that includes two exhaust passages connected with the respective banks of cylinders of a V-type internal combustion engine, a catalyst arranged in each exhaust passage, and a communication passage connecting the two exhaust passages with each other at a location upstream of the respective catalysts.